These hard frosts make it the ideal time for winter sowing. Some seeds have a hard seedcoat which germinates best after it has frozen and thawed repeatedly. Instructions on the backs of seed packets often suggest putting seeds in the freezer before sowing. This is fine in theory but it is actually the repeated freeze/thaw of a winter which degrades the seedcoat and allows germination. So sowing now and letting the seedtray repeatedly freeze will give the best results.
Obviously this only works with certain seeds - I winter sow larkspur, bells of ireland (Molucella laevis) and some hardy biennials like the black leaved cow parsley Anthriscus sylvestris 'ravenswing'. It will work with most hardy annuals but not with anything likely to be killed off by frost. It is really not worth it for easily germinated seeds such as calendula or cornflower The seedlings generally germinate in early spring and can then be pricked out and grown on. I actually tend to move the seedlings under cover at that point to keep them out of the wet which is more likely to kill them than the cold. It is nice to feel that you are able to do some gardening in the cold weather
I do not grow many perennials from seed but this is also the best way to grow a lot of hardy perennials - just remember to label all the seed trays.